Space Physiology - Bone and muscle loss in space

Microgravity is a challenging environment for the human organism. In particular, the mechanical loading of muscles and bones in the back, the hip area, and the legs is severely reduced in microgravity compared to earthbound conditions. This leads to sarcopenia and osteoporosis. For long-term spaceflight, the deconditioning of the musculo-skeletal system belongs to the most risky physiological changes observed in response to microgravity. To obtain health and effectiveness of astronauts especially for planned long-duration space flights, it is mandatory to develop efficient countermeasures. Current countermeasures are either less effective or too time-consuming for application during long-term mission. New developments are mandatory in order to keep muscle and bone function during the astronauts’ long-term flight.

Bone and muscle loss in space

Microgravity is a challenging environment for the human organism. In particular, the mechanical loading of muscles and bones in the back, the hip area, and the legs is severely reduced in microgravity compared to earthbound conditions. This leads to sarcopenia and osteoporosis. For long-term spaceflight, the deconditioning of the musculo-skeletal system belongs to the most risky physiological changes observed in response to microgravity. To obtain health and effectiveness of astronauts especially for planned long-duration space flights, it is mandatory to develop efficient countermeasures. Current countermeasures are either less effective or too time-consuming for application during long-term mission. New developments are mandatory in order to keep muscle and bone function during the astronauts’ long-term flight.

However, the observed changes are comparable to processes observed during ageing or in handicapped people with inborn or chronic diseases of the neuro-musculo-skeletal system. Insofar, the foreseen projects will aim at astronauts, ageing people and patients. Under consideration are special training measurements and nutraceuticals with a postulated positive effect on muscle and/or bone mass and function. To conduct research in this field on Earth, methods using 6° head-down tilt bed rest (HDTBR) as a simulation model for muscle and bone unloading (immobilization) are utilized.

The adequate stimulus for muscle growth keeping or increasing muscle trophy and strength is a given by a combination of high intense muscle contraction and passive stretches. These stimuli are e.g. provided by concentric-eccentric resistive exercise or by jumps and landings. Bone growth is locally triggered by strain and the best strain pattern in a bone is naturally generated by high intense muscle work or by impacts like the heel impact on ground during running.

A most time efficient training of all leg muscles is given by a leg press like apparatus. In microgravity, heavy weights cannot provide counter forces for muscle training. Existing, even newly developed training devices do not fulfil the required efficiency of a training method for microgravity. We therefore intend to verify and apply a Sensodrive-leg press as an upgrade and technological progress of the current flywheel device. Robotic controlled Sensodrives have originally been developed for ultra light weight robotic arms on the ISS. This novel technology combined with a leg press allows the application of various patterns of force and velocity at any angle of the hips, the knees, or the ankles during leg movement. During training the subject must not adapt to the physical properties of the device, but like a physiotherapist the device with its one intelligent robotic motor control also adapts to the needs of the subject. Time optimized and variable training stimuli and protocols can be developed, that provide optimum intense and maximum save stimuli for all groups of leg muscles and bones. The simulation of naturally earth bound situations like hopping or trampoline jumping will potentially also keep up motor control and balance. Little is known about the interrelations between muscle fatigue and the growth stimulus of training. The combination of the Sensodrive leg press and a lower body negative pressure device will be built to study the effects of alterations in muscle perfusion by gravity independent simulation of various levels of orthostasis.